The present invention relates in general to piston cooling nozzles and the manner of assembly and use of a piston cooling nozzle relative to an engine piston. More specifically the present invention relates to a piston cooling nozzle with a plurality of separated flow passageways which are designed to improve the targeting of the exiting spray plume against or into a desired area of the piston.
It is generally recognized that some small percentage of the heat available in the fuel will be absorbed by the pistons. While this percentage is only in the 3 to 8 percent range for aluminum alloy pistons, there is still a noticeable rise in the temperature of the piston due to this heat absorption. While there will be some heat transfer away from the piston and hence some cooling, additional cooling is frequently needed to keep the piston temperature within a safe range. The heat already being transferred comes from the rings, the land and skirt portions of the piston, and is transferred to the water jacket and to the crankcase oil by means of conduction. A splash or spray mist of crankcase oil is the conduit for this portion of the heat transfer. If higher than desired piston temperatures occur and there is insufficient cooling, the result will be increased crown, top land and top groove carbon deposits. As a general rule, top groove temperatures greater than 220 degrees C. (428 degrees F.) are considered excessive.
Under certain conditions some form of oil cooling of the piston becomes virtually essential to ensure satisfactory operation. One technique which is used to enable additional cooling by way of oil cooling is to provide a special oil feed/jet arrangement in combination with a specific piston design. While there are a variety of arrangements, the gallery-type of supplemental oil cooling may be the most popular. With this approach, a single-passageway nozzle is directed up into the piston and a divergent, non-targeted plume of oil is sprayed onto the underside of the piston. The divergent, non-targeted spray results in some portion of the oil being sprayed against piston surfaces which are not critical and which are not the preferred surfaces for the most effective cooling and heat transfer. When the piston is a galleried type, the preferred location for the plume of oil is directly into the gallery. However, with a divergent, non-targeted spray pattern, only a small portion of the cooling oil will actually be sprayed into the gallery. It is possible by the use of a properly designed test fixture to evaluate the collection efficiency for a particular piston cooling nozzle design. Such a test fixture provides the ability to compare competing nozzle designs relative to their collection efficiency.
The present invention improves upon the current designs for piston cooling nozzles by providing a new nozzle design that creates a targeted oil jet plume. With a targeted spray, it is easier to position and direct the spray to a localized and specific area of the piston such as a piston gallery opening. A related design challenge with regard to the present invention involved trying to adapt the new piston cooling nozzle into the existing engine design as an upgraded and improved replacement for the existing, less efficient piston cooling nozzles. In such a situation, the design of the engine block, cylinder liner, and crank counterweights are all fixed. Therefore, there are specific structural and dimensional constraints which have to be factored into the piston cooling nozzle design. Whether or not a piston cooling nozzle is already present in the engine design, it is important when providing an improved nozzle design that it be able to assemble into the engine without requiring any other modifications, redesign, or major disassembly. The ease of assembly and servicing are important factors to consider as well as the configuration and tolerancing of the nozzle relative to production costs.
The present invention has addressed the non-targeted spray pattern problem as well as the ease of assembly and cost concerns. The resulting invention structure achieves various objectives in a novel and unobvious manner. By means of a suitable test fixture it has been found that the invention achieves a collection efficiency of over 87 percent. This number refers to the volume of cooling oil which is collected into the piston cooling gallery relative to the total oil which is sprayed at the piston.
Since a variety of flow nozzle designs have been patented, including piston cooling nozzles, it may be helpful for an understanding of the present invention and its uniqueness and novelty to review some of these earlier design attempts. Listed below are three United States patents which are believed to be a representative sampling of these earlier nozzle designs:
______________________________________ PATENT NO. PATENTEE ISSUE DATE ______________________________________ 3,359,864 Hamlin Dec. 26, 1967 4,408,575 Clairmont, Jr. Oct. 11, 1983 4,508,065 Suchdev Apr. 2, 1985 ______________________________________
In addition to earlier patents, some piston cooling nozzle designs are disclosed in the technical literature. In the reference book entitled "Diesel Engine Reference Book" (Butterworth & Company Ltd., 1984), the editing author LRC Lilly describes various piston designs and types on pages 12-4 through 12-9. In Figure 12.4, a traditional oil feed/jet arrangement is shown.
An important part of the present invention involves the specific nozzle design which has been invented. As such it is helpful to understand that by separating a single turbulent flow stream of cooling oil into a plurality of smaller more laminar flow streams, the same volume of oil can be provided, but the spray divergence will be reduced, enabling more targeted jets of oil. The various jets of oil are still all targeted at virtually the same point, but an increase in the length to diameter ratio results in a jet with less radial divergence (i.e., decreased cone angle). With regard to specific nozzle designs, the three previously listed patent references may be of interest. Even though there may be several examples of piston cooling nozzles and assembly arrangements, the present invention remains novel and unobvious.